linux-kernel - Re: [RFC] respect the referenced bit of KVM guest pages?

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Date:	Wed, 19 Aug 2009 21:25:56 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Jeff Dike <jdike@...toit.com>, Avi Kivity <avi@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Yu, Wilfred" <wilfred.yu@...el.com>,
	"Kleen, Andi" <andi.kleen@...el.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [RFC] respect the referenced bit of KVM guest pages?

On Wed, Aug 19, 2009 at 9:10 PM, Wu Fengguang<fengguang.wu@...el.com> wrote:
> On Wed, Aug 19, 2009 at 08:05:19PM +0800, KOSAKI Motohiro wrote:
>> >> page_referenced_file?
>> >> I think we should change page_referenced().
>> >
>> > Yeah, good catch.
>> >
>> >>
>> >> Instead, How about this?
>> >> ==============================================
>> >>
>> >> Subject: [PATCH] mm: stop circulating of referenced mlocked pages
>> >>
>> >> Currently, mlock() systemcall doesn't gurantee to mark the page PG_Mlocked
>> >
>> >                                                    mark PG_mlocked
>> >
>> >> because some race prevent page grabbing.
>> >> In that case, instead vmscan move the page to unevictable lru.
>> >>
>> >> However, Recently Wu Fengguang pointed out current vmscan logic isn't so
>> >> efficient.
>> >> mlocked page can move circulatly active and inactive list because
>> >> vmscan check the page is referenced _before_ cull mlocked page.
>> >>
>> >> Plus, vmscan should mark PG_Mlocked when cull mlocked page.
>> >
>> >                           PG_mlocked
>> >
>> >> Otherwise vm stastics show strange number.
>> >>
>> >> This patch does that.
>> >
>> > Reviewed-by: Wu Fengguang <fengguang.wu@...el.com>
>>
>> Thanks.
>>
>>
>>
>> >> Index: b/mm/rmap.c
>> >> ===================================================================
>> >> --- a/mm/rmap.c       2009-08-18 19:48:14.000000000 +0900
>> >> +++ b/mm/rmap.c       2009-08-18 23:47:34.000000000 +0900
>> >> @@ -362,7 +362,9 @@ static int page_referenced_one(struct pa
>> >>        * unevictable list.
>> >>        */
>> >>       if (vma->vm_flags & VM_LOCKED) {
>> >> -             *mapcount = 1;  /* break early from loop */
>> >> +             *mapcount = 1;          /* break early from loop */
>> >> +             *vm_flags |= VM_LOCKED; /* for prevent to move active list */
>> >
>> >> +             try_set_page_mlocked(vma, page);
>> >
>> > That call is not absolutely necessary?
>>
>> Why? I haven't catch your point.
>
> Because we'll eventually hit another try_set_page_mlocked() when
> trying to unmap the page. Ie. duplicated with another call you added
> in this patch.

Yes. we don't have to call it and we can make patch simple.
I already sent patch on yesterday.

http://marc.info/?l=linux-mm&m=125059325722370&w=2

I think It's more simple than KOSAKI's idea.
Is any problem in my patch ?


>
> Thanks,
> Fengguang
>
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-- 
Kind regards,
Minchan Kim
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